1. Field of the Invention
This invention relates generally to improvements in memory addressing, and relates more specifically to a system and method for frame and field memory access operations within a wide-word memory.
2. Description of the Background Art
Controllers for digital audio and digital video information must rapidly manipulate substantial amounts of data. A common architectural approach to facilitate this data manipulation is to organize the memory so that it transfers the data in wide words. In this manner, many bytes of data may be transferred simultaneously during a single memory access. It is desirable for direct memory access (DMA) transfers to be organized to allow multiple wide-word transfers with little intervention from functional units processing the digital audio and video.
One common format for storing and presenting digital audio and video information is Moving Picture Experts Group version 2 (MPEG-2). MPEG-2 has been chosen as the video format for digital video disks (DVD) and digital television (DTV). The MPEG-2 format achieves substantial data compression by recognizing the existence of spatial and temporal redundancy in moving pictures, and then omitting these redundant elements. Spatial redundancy is reduced by a process that includes performing a discrete cosine transform on a matrix of adjacent picture elements (pixels). The MPEG-2 specification has standardized the size of this matrix as 8-by-8 pixels, and named this matrix a "block". An MPEG-2 block should not be confused with an MPEG-2 "macroblock" used to reduce temporal redundancy. Because of the defined blocks in MPEG-2, manipulating arrays of data in memory corresponding to these blocks is an important consideration in digital video controllers for MPEG-2-formatted video.
A controller for MPEG-2 video on a DVD has an additional concern. A DVD player may be connected to either an interlaced or a non-interlaced (progressive-scan) video display. An interlaced video display shows two alternating fields of display lines, odd and even, to produce a single frame of video. A progressive-scan video display shows a single frame of consecutive display lines. An example of an interlaced video display is a standard analog television set, and an example of a progressive-scan video display is a computer display monitor. A recorded DVD disk may need to be displayed on either an interlaced or a progressive-scan display. For this reason, it may be necessary for a controller of MPEG-2 video on a DVD to rapidly convert digital data organized by frames (for progressive-scan displays) into digital data organized by fields (for interlaced displays). Therefore, techniques for rapidly manipulating substantial amounts of data remain a significant consideration in memory addressing operations.